In the Goes Wrong Show episode ‘Harper’s Locket’, we learn that Max is writing a play called Dr Frog. In the same episode, we learn that frogs are the only thing Annie can paint.
I like to think that this is what happened:
Max: Hey, Annie! I wanted to talk to you. I’m writing a play about a doctor.
Annie: Oh, that’s great! Give me a good part.
Max: You seem artistic; I thought maybe you could do a painting for the poster.
Annie: I’m flattered, thanks, but frogs are the only thing I can paint.
Max: No problem; I just had an incredible idea.